System for Grading Filling of a Hydraulic Suspension System

ABSTRACT

A system for grading filling of a suspension system includes: a pump control module configured to, during first and second periods, operate an electric pump of the suspension system in first and second directions and decreasing and increasing hydraulic fluid pressure within the suspension system, respectively; a monitoring module configured to: store a first pressure of hydraulic fluid within the suspension system measured using a pressure sensor when the first pressure is less than or equal a first predetermined pressure while the pump is operated in the first direction; and store a second pressure measured using the pressure sensor when the second pressure is greater than or equal a second predetermined pressure while the pump is operated in the second direction; and a grade module configured to determine a grade value for the filling of the suspension system based on the first and second pressures.

FIELD

The present disclosure relates generally to suspension systems for motorvehicles and more particularly to suspension systems that resist thepitch and roll movements of a vehicle.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Suspension systems improve the ride of a vehicle by absorbing bumps andvibrations that would otherwise unsettle the vehicle body. Suspensionsystems also improve safety and control by improving contact between theground and the tires of the vehicle. One drawback of suspension systemsis that basic spring/damper arrangements will allow the vehicle toroll/lean right or left during corning (e.g., in turns), pitch forwardunder deceleration (e.g., under braking), and pitch back underacceleration. The lateral acceleration the vehicle experiences in turnscauses a roll moment where the vehicle will lean/squat to the right whenturning left and to the left when turning right. The fore and aftacceleration the vehicle experiences under acceleration and brakingcauses a pitch moment where the vehicle will lean forward loading thefront axle during braking and aft, loading the rear axle, underacceleration. These roll and pitch moments decrease grip, corneringperformance, and braking performance and can also be uncomfortable tothe driver and passengers. Many vehicles are equipped with stabilizerbars/anti-roll bars, which are mechanical systems that help counteractthe roll and/or pitch moments experienced during driving. For example,anti-roll bars are typically mechanical linkages that extend laterallyacross the width of the vehicle between the right and left dampers. Whenone of the dampers extends, the anti-roll bar applies a force to theopposite damper that counteracts the roll moment of the vehicle andhelps to correct the roll angle to provide flatter cornering. However,there are several drawbacks associated with these mechanical systems.First, there are often packaging constraints associated with mechanicalsystems because a stabilizer bar/anti-roll bar requires a relativelystraight, unobstructed path across the vehicle between the dampers.Second, stabilizer bars/anti-roll bars are reactive and work when thesuspension starts moving (i.e. leaning). Such mechanical systems cannotbe easily switched off or cancelled out when roll stiffness is not need.Some vehicles do have stabilizer bar/anti-roll bar disconnects that maybe manually or electronically actuated, but the complexity and costassociated with these systems may make them ill-suited for most vehicleapplications.

In an effort to augment or replace traditional mechanical stabilizerbars/anti-roll bars, anti-roll suspension systems are being developedthat hydraulically connect two or more dampers in a hydraulic circuitwhere the extension of one damper produces a pressure change in theother damper(s) in the hydraulic circuit that makes it more difficult tocompress the other damper(s) in the hydraulic circuit. This pressurechange in the other damper(s) increases the roll stiffness of thesuspension system of the vehicle. However, the downside of such systemsis that ride comfort is more difficult to achieve because bump forcescan be transmitted from one damper to another damper across thehydraulic circuit resulting in unwanted suspension movement.Accordingly, there remains a need for improved vehicle suspensionsystems that can minimize pitch and roll while maintaining acceptablelevels of ride comfort.

SUMMARY

In a feature, a system for grading filling of a suspension system withhydraulic fluid includes: a pump control module configured to: during afirst period, operate an electric pump of the suspension system in afirst direction and decrease hydraulic fluid pressure within thesuspension system; and during a second period, operate the electric pumpof the suspension system in a second direction and increase hydraulicfluid pressure within the suspension system; a monitoring moduleconfigured to: store a first pressure of hydraulic fluid within thesuspension system measured using a pressure sensor when the firstpressure is less than or equal a first predetermined pressure while thepump is operated in the first direction; and store a second pressure ofhydraulic fluid within the suspension system measured using the pressuresensor when the second pressure is greater than or equal a secondpredetermined pressure while the pump is operated in the seconddirection; and a grade module configured to determine a grade value forfilling of the suspension system with hydraulic fluid based on the firstpressure and the second pressure.

In further features, the second predetermined pressure is greater thanthe first predetermined pressure.

In further features, the first period is before the second period.

In further features, an indicator module is configured to: set anindicator to a first state when the grade value is greater than apredetermined value; and set the indicator to a second state when thegrade value is less than the predetermined value.

In further features, an air module is configured to determine a volumeof air in the suspension system based on the first pressure and thesecond pressure, where the grade module is configured to determine thegrade value for filling of the suspension system with hydraulic fluidbased on the volume of air in the suspension system.

In further features, the grade module is configured to: decrease thegrade value as the volume of air increases; and increase the grade valueas the volume of air decreases.

In further features, the grade module is configured to determine thegrade value for filling of the suspension system with hydraulic fluidbased on the volume of air in the suspension system and a predeterminedtotal volume of the suspension system.

In further features, the grade module is configured to set the gradevalue based on the equation:

$\frac{Vt - Va}{Vt},$

where Vt is the predetermined total volume of the suspension system andVa is the volume of air in the suspension system.

In further features, the grade module is configured to: determine avolume of hydraulic fluid in the suspension system based on the firstpressure and the second pressure; and determine the grade value forfilling of the suspension system with hydraulic fluid based on thevolume of hydraulic fluid in the suspension system.

In further features, the grade module is configured to: decrease thegrade value as the volume of air increases; and increase the grade valueas the volume of air decreases.

In further features, the grade module is configured to determine thegrade value for filling of the suspension system with hydraulic fluidbased on the volume of oil in the suspension system and a predeterminedtotal volume of the suspension system.

In further features, the grade module is configured to set the gradevalue based on the equation:

$\frac{Vh}{Vt},$

where Vt is the predetermined total volume of the suspension system andVh is the volume of hydraulic fluid in the suspension system.

In a feature, a method of grading filling of a suspension system withhydraulic fluid includes: during a first period, operating an electricpump of the suspension system in a first direction and decreasehydraulic fluid pressure within the suspension system; during a secondperiod, operating the electric pump of the suspension system in a seconddirection and increase hydraulic fluid pressure within the suspensionsystem; storing a first pressure of hydraulic fluid within thesuspension system measured using a pressure sensor when the firstpressure is less than or equal a first predetermined pressure while thepump is operated in the first direction; storing a second pressure ofhydraulic fluid within the suspension system measured using the pressuresensor when the second pressure is greater than or equal a secondpredetermined pressure while the pump is operated in the seconddirection; and determining a grade value for filling of the suspensionsystem with hydraulic fluid based on the first pressure and the secondpressure.

In further features, the second predetermined pressure is greater thanthe first predetermined pressure.

In further features, the first period is before the second period.

In further features, the method further includes: setting an indicatorto a first state when the grade value is greater than a predeterminedvalue; and setting the indicator to a second state when the grade valueis less than the predetermined value.

In further features, the method further includes determining a volume ofair in the suspension system based on the first pressure and the secondpressure, where determining the grade value includes determining thegrade value for filling of the suspension system with hydraulic fluidbased on the volume of air in the suspension system.

In further features, determining the grave value includes: decreasingthe grade value as the volume of air increases; and increasing the gradevalue as the volume of air decreases.

In further features, determining the grade value includes determiningthe grade value for filling of the suspension system with hydraulicfluid based on the volume of air in the suspension system and apredetermined total volume of the suspension system.

In further features, determining the grade value includes setting thegrade value based on the equation:

$\frac{Vt - Va}{Vt},$

where Vt is the predetermined total volume of the suspension system andVa is the volume of air in the suspension system.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic diagram illustrating an example suspension systemthat includes two comfort valves that open and close the hydraulic linesconnecting the two front dampers to the two rear dampers of the system;

FIG. 2 is a schematic diagram illustrating an example suspension systemthat includes two comfort valves that open and close the hydraulic linesconnecting the two front dampers to the two rear dampers of the systemand a separate hydraulic lifting circuit for the two front dampers;

FIG. 3 is a schematic diagram illustrating an example suspension systemthat includes two comfort valves that open and close the hydraulic linesconnecting the two front dampers to the two rear dampers of the systemand two separate hydraulic lifting circuits for the two front dampersand the two rear dampers;

FIG. 4 is a schematic diagram illustrating an example suspension systemthat includes four hydraulic circuits connecting the front and reardampers and an example comfort valve equipped manifold assembly;

FIG. 5 is a schematic diagram illustrating the example comfort valveequipped manifold assembly illustrated in FIG. 4 ;

FIG. 6 is a schematic diagram illustrating an example suspension systemthat includes four hydraulic circuits connecting the front and reardampers and an example comfort valve equipped manifold assembly;

FIG. 7 is a schematic diagram illustrating an example suspension systemthat includes four hydraulic circuits connecting the front and reardampers and an example comfort valve equipped manifold assembly;

FIG. 8 includes a functional block diagram of an example implementationof a suspension control module;

FIG. 9 is a functional block diagram of an example implementation of agrading module; and

FIG. 10 is a flowchart depicting an example method of grading a fillingof a suspension system with hydraulic fluid.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

With reference to FIG. 1 , a suspension system 100 including a frontleft damper 102 a, a front right damper 102 b, a back left damper 102 c,and a back right damper 102 d. While it should be appreciated that thesuspension system 100 described herein may include a different number ofdampers than those shown in the drawings, in most automotiveapplications, four dampers are used at each corner of a vehicle tocontrol vertical movements of the front and rear wheels of the vehicle.Thus, the front left damper 102 a controls (e.g., dampens) up and down(i.e., vertical) movements of the front left wheel of the vehicle, thefront right damper 102 b controls (e.g., dampens) up and down (i.e.,vertical) movements of the front right wheel of the vehicle, the backleft damper 102 c controls (e.g., dampens) up and down (i.e., vertical)movements of the back left wheel of the vehicle, and the back rightdamper 102 d controls (e.g., dampens) up and down (i.e., vertical)movements of the back right wheel of the vehicle.

The suspension system 100 also includes a manifold assembly 104 that isconnected in fluid communication with a pump assembly 106 by a pumphydraulic line 108. Although other configurations are possible, in theillustrated example, the pump assembly 106 includes a bi-directionalpump 110, a hydraulic reservoir 112 (e.g., a tank), and a bypasshydraulic line 114 that can be open and closed by a pressure reliefvalve 116. The bi-directional pump 110 includes a first inlet/outletport that is connected to the pump hydraulic line 108 and a secondinlet/outlet port that is connected in fluid communication with thehydraulic reservoir 112 by a reservoir hydraulic line 118. Thebi-directional pump 110 may operate (i.e., pump fluid) in two oppositedirections depending on the polarity of the electricity that is suppliedto the pump 110, so the first inlet/outlet port may operate as either aninlet port or an outlet port depending on the direction thebi-directional pump 110 is operating in and the same is true for thesecond inlet/outlet port of the bi-directional pump 110. In the examplewhere the first inlet/outlet port is operating as an inlet port for thebi-directional pump 110 and the second inlet/outlet port is operating asan outlet port for the bi-directional pump 110, the bi-directional pump110 draws in hydraulic fluid from the pump hydraulic line 108 via thefirst inlet/outlet port and discharges hydraulic fluid into thereservoir hydraulic line 118 via the second inlet/outlet port. As such,the bi-directional pump 110 produces a negative pressure in the pumphydraulic line 108 that can be used by manifold assembly 104 to reducedfluid pressure in the suspension system 100. In the example where thesecond inlet/outlet port is operating as an inlet port for thebi-directional pump 110 and the first inlet/outlet port is operating asan outlet port for the bi-directional pump 110, the bi-directional pump110 draws in hydraulic fluid from the reservoir hydraulic line 118 viathe second inlet/outlet port and discharges hydraulic fluid into thepump hydraulic line 108 via the first inlet/outlet port. As such, thebi-directional pump 110 produces a positive pressure in the pumphydraulic line 108 that can be used by manifold assembly 104 to increasefluid pressure in the suspension system 100. The bypass hydraulic line114 runs from the pump hydraulic line 108 to the hydraulic reservoir 112and bleeds fluid back into the hydraulic reservoir 112 when the pressurein the pump hydraulic line 108 exceeds a threshold pressure that causesthe pressure relief valve 116 to open.

The manifold assembly 104 is connected in fluid communication with thefront and rear dampers 102 a, 102 b, 102 c, 102 d by first and secondhydraulic circuits 120 a, 120 b. The manifold assembly 104 includesfirst and second manifold valves 122 a, 122 b that are connected inparallel with the pump hydraulic line 108. The first hydraulic circuit120 a is connected in fluid communication with the first manifold valve122 a and the second hydraulic circuit 120 b is connected in fluidcommunication with the second manifold valve 122 b. The manifoldassembly 104 also includes a first pressure sensor 124 a that isarranged to monitor the pressure in the first hydraulic circuit 120 aand a second pressure sensor 124 b that is arranged to monitor thepressure in the second hydraulic circuit 120 b. The bi-directional pump110 of the pump assembly 106 and first and second pressure sensors 124a, 124 b and the first and second manifold valves 122 a, 122 b of themanifold assembly 104 are electrically connected to a suspension controlmodule 123, which is configured to activate (i.e., turn on in forward orreverse) the bi-directional pump 110 and electronically actuate (i.e.,open and close) the first and second manifold valves 122 a, 122 b inresponse to various inputs, including signals from the first and secondpressure sensors 124 a, 124 b. When the suspension control module 123opens the first and second manifold valves 122 a, 122 b, the fluidpressure in the first and second hydraulic circuits 120 a, 120 bincreases or decreases, respectively, depending on which direction thebi-directional pump 110 is running in.

The anti-pitch and anti-roll capabilities of the suspension system 100will be explained in greater detail below. However, from FIG. 1 itshould be appreciated that fluid pressure in the first and secondhydraulic circuits 120 a, 120 b operate to dynamically adjust the rolland pitch stiffness of the vehicle and can be used to either augment orcompletely replace mechanical stabilizer bars/anti-roll bars. Suchmechanical systems require relatively straight, unobstructed runsbetween each of the front dampers 102 a, 102 b and each of the backdampers 102 c, 102 d. Accordingly, the suspension system 100 disclosedherein offers packaging benefits because the dampers 102 a, 102 b, 102c, 102 d only need to be hydraulically connected to the manifoldassembly 104 and to the suspension control module 123.

Each of the dampers 102 a, 102 b, 102 c, 102 d of the suspension system100 includes a damper housing, a piston rod, and a piston that ismounted on the piston rod. The piston is arranged in sliding engagementwith the inside of the damper housing such that the piston divides thedamper housing into compression and rebound chambers. As such, the frontleft damper 102 a includes a first compression chamber 126 a and a firstrebound chamber 128 a, the front right damper 102 b includes a secondcompression chamber 126 b and a second rebound chamber 128 b, the backleft damper 102 c includes a third compression chamber 126 c and a thirdrebound chamber 128 c, and the back right damper 102 d includes a fourthcompression chamber 126 d and a fourth rebound chamber 128 d.

In each damper 102 a, 102 b, 102 c, 102 d, the piston is a closed pistonwith no fluid flow paths defined within or by its structure. Inaddition, there are no other fluid flow paths in the damper housing suchthat no fluid is communicated between the compression and reboundchambers of the dampers 102 a, 102 b, 102 c, 102 d except through thefirst and second hydraulic circuits 120 a, 120 b. The rebound chambers128 a, 128 b, 128 c, 128 d of the dampers 102 a, 102 b, 102 c, 102 ddecrease in volume during rebound/extension strokes and increase involume during compression strokes of the dampers 102 a, 102 b, 102 c,102 d. The compression chambers 126 a, 126 b, 126 c, 126 d of thedampers 102 a, 102 b, 102 c, 102 d decrease in volume during compressionstrokes of the dampers 102 a, 102 b, 102 c, 102 d and increase in volumeduring rebound/extension strokes of the dampers 102 a, 102 b, 102 c, 102d.

Each damper 102 a, 102 b, 102 c, 102 d also includes rebound andcompression chamber ports 130 a, 130 b in the damper housing that areeach provided with dampening valves. The rebound chamber port 130 a isarranged in fluid communication with the rebound chamber 128 a, 128 b,128 c, 128 d of the damper 102 a, 102 b, 102 c, 102 d and the secondport 130 b is arranged in fluid communication with the compressionchamber 126 a, 126 b, 126 c, 126 d of the damper 102 a, 102 b, 102 c,102 d. The dampening valves in the rebound and compression chamber ports130 a, 130 b can be passive / spring-biased valves (e.g., spring-discstacks) or active valves (e.g., electromechanical valves) and controlfluid flow into and out of the compression and rebound chambers of thedampers 102 a, 102 b, 102 c, 102 d to provide one or more rebounddampening rates and compression dampening rates for each of the dampers102 a, 102 b, 102 c, 102 d.

The first hydraulic circuit 120 a includes a first longitudinalhydraulic line 132 a that extends between and fluidly connects thesecond port 130 b (to the first compression chamber 126 a) of the frontleft damper 102 a and the second port 130 b (to the third compressionchamber 126 c) of the back left damper 102 c. The first hydrauliccircuit 120 a includes a front hydraulic line 134 a that extends betweenand fluidly connects the first longitudinal hydraulic line 132 a and therebound chamber port 130 a (to the second rebound chamber 128 b) of thefront right damper 102 b. The first hydraulic circuit 120 a alsoincludes a rear hydraulic line 136 a that extends between and fluidlyconnects the first longitudinal hydraulic line 132 a and the reboundchamber port 130 a (to the fourth rebound chamber 128 d) of the backright damper 102 d. The first hydraulic circuit 120 a further includes afirst manifold hydraulic line 138 a that extends between and fluidlyconnects the first longitudinal hydraulic line 132 a and the firstmanifold valve 122 a. The second hydraulic circuit 120 b includes asecond longitudinal hydraulic line 132 b that extends between andfluidly connects the compression chamber port 130 b (to the secondcompression chamber 126 b) of the front right damper 102 b and thecompression chamber port 130 b (to the fourth compression chamber 126 d)of the back right damper 102 d. The second hydraulic circuit 120 bincludes a front hydraulic line 134 b that extends between and fluidlyconnects the second longitudinal hydraulic line 132 b and the reboundchamber port 130 a (to the first rebound chamber 128 a) of the frontleft damper 102 a. The second hydraulic circuit 120 b also includes arear hydraulic line 136 b that extends between and fluidly connects thesecond longitudinal hydraulic line 132 b and the rebound chamber port130 a (to the third rebound chamber 128 c) of the back left damper 102c. The second hydraulic circuit 120 b further includes a second manifoldhydraulic line 138 b that extends between and fluidly connects thesecond longitudinal hydraulic line 132 b and the second manifold valve122 b. It should be appreciated that the word “longitudinal” as used inthe first and second longitudinal hydraulic lines 132 a, 132 b simplymeans that the first and second longitudinal hydraulic lines 132 a, 132b run between the front dampers 102 a, 102 b and the back dampers 102 c,102 d generally. The first and second longitudinal hydraulic lines 132a, 132 b need not be linear or arranged in any particular direction aslong as they ultimately connect the front dampers 102 a, 102 b and theback dampers 102 c, 102 d.

The suspension system 100 also includes four bridge hydraulic lines 140a, 140 b, 140 c, 140 d that fluidly couple the first and secondhydraulic circuits 120 a, 120 b and each corner of the vehicle. The fourbridge hydraulic lines 140 a, 140 b, 140 c, 140 d include a front leftbridge hydraulic line 140 a that extends between and fluidly connectsthe first longitudinal hydraulic line 132 a of the first hydrauliccircuit 120 a and the front hydraulic line 134 b of the second hydrauliccircuit 120 b, a front right bridge hydraulic line 140 b that extendsbetween and fluidly connects the front hydraulic line 134 a of the firsthydraulic circuit 120 a and the second longitudinal hydraulic line 132 bof the second hydraulic circuit 120 b, a back left bridge hydraulic line140 c that extends between and fluidly connects the first longitudinalhydraulic line 132 a of the first hydraulic circuit 120 a and the rearhydraulic line 136 b of the second hydraulic circuit 120 b, and a backright bridge hydraulic line 140 d that extends between and fluidlyconnects the rear hydraulic line 136 a of the first hydraulic circuit120 a and the second longitudinal hydraulic line 132 b of the secondhydraulic circuit 120 b.

The front left bridge hydraulic line 140 a is connected to the firstlongitudinal hydraulic line 132 a between the compression chamber port130 b of the front left damper 102 a and the front hydraulic line 134 aof the first hydraulic circuit 120 a. The front right bridge hydraulicline 140 b is connected to the second longitudinal hydraulic line 132 bbetween the compression chamber port 130 b of the front right damper 102b and the front hydraulic line 134 b of the second hydraulic circuit 120b. The back left bridge hydraulic line 140 c is connected to the firstlongitudinal hydraulic line 132 a between the compression chamber port130 b of the back left damper 102 c and the rear hydraulic line 136 a ofthe first hydraulic circuit 120 a. The back right bridge hydraulic line140 d is connected to the second longitudinal hydraulic line 132 bbetween the compression chamber port 130 b of the back right damper 102d and the rear hydraulic line 136 b of the second hydraulic circuit 120b. In the illustrated example, the various hydraulic lines are made offlexible tubing (e.g., hydraulic hoses), but it should be appreciatedthat other conduit structures and/or fluid passageways can be used.

A front left accumulator 142 a is arranged in fluid communication withthe first longitudinal hydraulic line 132 a at a location between thecompression chamber port 130 b of the front left damper 102 a and thefront left bridge hydraulic line 140 a. A front right accumulator 142 bis arranged in fluid communication with the second longitudinalhydraulic line 132 b at a location between the compression chamber port130 b of the front right damper 102 b and the front right bridgehydraulic line 140 b. A back left accumulator 142 c is arranged in fluidcommunication with the first longitudinal hydraulic line 132 a at alocation between the compression chamber port 130 b of the back leftdamper 102 c and the back left bridge hydraulic line 140 c. A back rightaccumulator 142 d is arranged in fluid communication with the secondlongitudinal hydraulic line 132 b at a location between the compressionchamber port 130 b of the back right damper 102 d and the back rightbridge hydraulic line 140 d. Each of the accumulators 142 a, 142 b, 142c, 142 d have a variable fluid volume that increases and decreasesdepending on the fluid pressure in the first and second longitudinalhydraulic lines 132 a, 132 b. It should be appreciated that theaccumulators 142 a, 142 b, 142 c, 142 d may be constructed in a numberof different ways. For example and without limitation, the accumulators142 a, 142 b, 142 c, 142 d may have accumulation chambers andpressurized gas chambers that are separated by floating pistons orflexible membranes.

The suspension system 100 also includes six electro-mechanical comfortvalves 144 a, 144 b, 144 c, 144 d, 146 a, 146 b that are connectedin-line (i.e., in series) with each of the bridge hydraulic lines 140 a,140 b, 140 c, 140 d and each of the longitudinal hydraulic lines 132 a,132 b. A front left comfort valve 144 a is positioned in the front leftbridge hydraulic line 140 a. A front right comfort valve 144 b ispositioned in the front right bridge hydraulic line 140 b. A back leftcomfort valve 144 c is positioned in the back left bridge hydraulic line140 c. A back right comfort valve 144 d is positioned in the back rightbridge hydraulic line 140 d. A first longitudinal comfort valve 146 a ispositioned in the first longitudinal hydraulic line 132 a between thefront and rear hydraulic lines 134 a, 136 a of the first hydrauliccircuit 120 a. A second longitudinal comfort valve 146 b is positionedin the second longitudinal hydraulic line 132 b between the front andrear hydraulic lines 134 b, 136 b of the second hydraulic circuit 120 b.In the illustrated example, the comfort valves 144 a, 144 b, 144 c, 144d and the longitudinal comfort valves 146 a, 146 b are semi-activeelectro-mechanical valves with a combination of passive spring-diskelements and a solenoid. The comfort valves 144 a, 144 b, 144 c, 144 dand the longitudinal comfort valves 146 a, 146 b are electronicallyconnected to the suspension control module 123, which is configured tosupply electrical current to the solenoids of the comfort valves 144 a,144 b, 144 c, 144 d and the longitudinal comfort valves 146 a, 146 b toselectively and individually open and close the comfort valves 144 a,144 b, 144 c, 144 d and the longitudinal comfort valves 146 a, 146 b.

The first pressure sensor 124 a of the manifold assembly 104 is arrangedto measure fluid pressure in the first manifold hydraulic line 138 a andthe second pressure sensor 124 b of the manifold assembly 104 isarranged to measure fluid pressure in the second manifold hydraulic line138 b. When the vehicle is cornering, braking, or accelerating, thelateral and longitudinal acceleration is measured by one or moreaccelerometers (not shown) and the anti-roll torque to control the rolland pitch of the vehicle is calculated by the suspension control module123. Alternatively, the lateral and longitudinal acceleration of thevehicle can be computed by the suspension control module 123 based on avariety of different inputs, including without limitation, steeringangle, vehicle speed, brake pedal position, and/or accelerator pedalposition. The dampers 102 a, 102 b, 102 c, 102 d are used to provideforces that counteract the roll moment induced by the lateral andlongitudinal acceleration, thus reducing the roll and pitch angles ofthe vehicle.

When the first and second manifold valves 122 a, 122 b are closed, thefirst and second hydraulic circuits 120 a, 120 b operate as a closedloop system, either together or separately depending on the open orclosed status of the electro-mechanical comfort valves 144 a, 144 b, 144c, 144 d and the longitudinal comfort valves 146 a, 146 b. When thefirst and/or second manifold valves 122 a, 122 b are open, thebi-directional pump 110 either adds or removes fluid from the firstand/or second hydraulic circuits 120 a, 120 b. As will be explained ingreater detail below, the suspension system 100 can control the rollstiffness of the vehicle, which changes the degree to which the vehiclewill lean to one side or the other during corning (i.e., roll)

For example, when the vehicle is put into a right-hand turn, themomentum of the sprung weight of the vehicle tends to make the vehiclelean left towards the outside of the turn, compressing the front leftdamper 102 a and the back left damper 102 c. When this occurs, fluidflows out from the first compression chamber 126 a of the front leftdamper 102 a and the third compression chamber 126 c of the back leftdamper 102 c into the first longitudinal hydraulic line 132 a of thefirst hydraulic circuit 120 a. As a result of the weight transfer to theleft side of the vehicle, the front right damper 102 b and back rightdamper 102 d begin to extend, causing fluid to flow out of the secondrebound chamber 128 b of the front right damper 102 b and the fourthrebound chamber 128 d of the back right damper 102 d into the front andrear hydraulic lines 134 a, 136 a of the first hydraulic circuit 120 a.When the comfort valves 144 a, 144 b, 144 c, 144 d are closed, the fluidflow out of the first compression chamber 126 a of the front left damper102 a, out of the third compression chamber 126 c of the back leftdamper 102 c, out of the second rebound chamber 128 b of the front rightdamper 102 b, and out of the fourth rebound chamber 128 d of the backright damper 102 d and into the front and rear hydraulic lines 134 a,136 a of the first hydraulic circuit 120 a increases the pressure in thefront left and back left accumulators 142 a, 142 c, thus providing apassive roll resistance where it becomes increasingly more difficult tocompress the front left damper 102 a and the back left damper 102 csince the first compression chamber 126 a of the front left damper 102 aand the third compression chamber 126 c of the back left damper 102 care connected in fluid communication with the first hydraulic circuit120 a. At the same time, fluid flows out of front left and back leftaccumulators 142 b, 142 d and into the first rebound chamber 128 a ofthe front left damper 102 a, into the third rebound chamber 128 c of theback left damper 102 c, into the second compression chamber 126 b of thefront right damper 102 b, and into the fourth compression chamber 126 dof the back right damper 102 d. The resulting pressure differencebetween the dampers 102 a, 102 b, 102 c, 102 d generates damper forcesthat counteract or resist the roll moment of the vehicle. Additionalroll resistance can be added by opening the first manifold valve 122 aas the bi-directional pump 110 is running in a first direction where thebi-directional pump 110 draws in hydraulic fluid from the reservoirhydraulic line 118 and discharges hydraulic fluid into the pumphydraulic line 108 to produce a positive pressure in the pump hydraulicline 108, which increases fluid pressure in the first hydraulic circuit120 a when the first manifold valve 122 a is open.

The opposite is true when the vehicle is put into a left-hand turn,where the momentum of the sprung weight of the vehicle tends to make thevehicle lean right towards the outside of the turn, compressing thefront right damper 102 b and the back right damper 102 d. When thisoccurs, fluid flows out from the second compression chamber 126 b of thefront right damper 102 b and the fourth compression chamber 126 d of theback right damper 102 d into the second longitudinal hydraulic line 132b of the second hydraulic circuit 120 b. As a result of the weighttransfer to the right side of the vehicle, the front left damper 102 aand back left damper 102 c begin to extend, causing fluid to flow out ofthe first rebound chamber 128 a of the front left damper 102 a and thethird rebound chamber 128 c of the back left damper 102 c into the frontand rear hydraulic lines 134 b, 136 b of the second hydraulic circuit120 b. When the comfort valves 144 a, 144 b, 144 c, 144 d are closed,the fluid flow out of the second compression chamber 126 b of the frontright damper 102 b, out of the fourth compression chamber 126 d of theback right damper 102 d, out of the first rebound chamber 128 a of thefront left damper 102 a, and out of the third rebound chamber 128 c ofthe back left damper 102 c and into the front and rear hydraulic lines134 b, 136 b of the second hydraulic circuit 120 b increases thepressure in the front right and back right accumulators 142 b, 142 d,thus providing a passive roll resistance where it becomes increasinglymore difficult to compress the front right damper 102 b and the backright damper 102 d since the second compression chamber 126 b of thefront right damper 102 b and the fourth compression chamber 126 d of theback right damper 102 d are connected in fluid communication with thesecond hydraulic circuit 120 b. At the same time, fluid flows out offront right and back right accumulators 142 a, 142 c and into the secondrebound chamber 128 b of the front right damper 102 b, into the fourthrebound chamber 128 d of the back right damper 102 d, into the firstcompression chamber 126 a of the front left damper 102 a, and into thethird compression chamber 126 c of the back left damper 102 c. Theresulting pressure difference between the dampers 102 a, 102 b, 102 c,102 d generates damper forces that counteract or resist the roll momentof the vehicle. Additional roll resistance can be added by opening thesecond manifold valve 122 b as the bi-directional pump 110 is running inthe first direction where the bi-directional pump 110 draws in hydraulicfluid from the reservoir hydraulic line 118 and discharges hydraulicfluid into the pump hydraulic line 108 to produce a positive pressure inthe pump hydraulic line 108, which increases fluid pressure in thesecond hydraulic circuit 120 b when the second manifold valve 122 b isopen.

When roll stiffness is not required, the comfort valves 144 a, 144 b,144 c, 144 d and the longitudinal comfort valves 146 a, 146 b can beopened to enhance the ride comfort of the suspension system 100 andreduce or eliminate unwanted suspension movements resulting from thehydraulic coupling of one damper of the system to another damper of thesystem (e.g., where the compression of one damper causes movement and/ora dampening change in another damper). For example, when the front leftcomfort valve 144 a is open and the front left damper 102 a undergoes acompression stroke as the front left wheel hits a bump, fluid may flowfrom the first compression chamber 126 a of the front left damper 102 a,into the first longitudinal hydraulic line 132 a, from the firstlongitudinal hydraulic line 132 a to the front hydraulic line 134 b ofthe second hydraulic circuit 120 b by passing through the front leftbridge hydraulic line 140 a and the front left comfort valve 144 a, andinto the first rebound chamber 128 a of the front left damper 102 a.Thus, fluid can travel from the first compression chamber 126 a to thefirst rebound chamber 128 a of the front left damper 102 a with the onlyrestriction coming from the dampening valves in the rebound andcompression chamber ports 130 a, 130 b of the front left damper 102 a.As such, when all of the comfort valves 144 a, 144 b, 144 c, 144 d andthe longitudinal comfort valves 146 a, 146 b are open, the dampers 102a, 102 b, 102 c, 102 d are effectively decoupled from one another forimproved ride comfort. It should also be appreciated that to return thesuspension system 100 to this “comfort mode” of operation, the firstand/or second manifold valves 122 a, 122 b may be opened while thebi-directional pump 110 is running in a second direction where thebi-directional pump 110 draws in hydraulic fluid from the pump hydraulicline 108 and discharges hydraulic fluid into the reservoir hydraulicline 118 to produce a negative pressure in the pump hydraulic line 108that reduces fluid pressure in the first and/or second hydrauliccircuits 120 a, 120 b.

FIG. 2 illustrates another suspension system 200 that shares many of thesame components as the suspension system 100 illustrated in FIG. 1 , butin FIG. 2 a front axle lift assembly 248 has been added. Rather thanrepeat the description set forth above, the following paragraphsdescribe the structure and function of the components in FIG. 2 that arenew and/or different from those shown and described in connection withFIG. 1 . It should be appreciated that the reference numbers in FIG. 1are “100” series numbers (e.g., 100, 102, 104, etc.) whereas thecomponents in FIG. 2 that are the same or similar to the components ofthe suspension system 100 shown in FIG. 1 share the same base referencenumbers, but are listed as “200” series numbers (e.g., 200, 202, 204,etc.). Thus, the same description for element 100 above applies toelement 200 in FIG. 2 and so on and so forth.

The front axle lift assembly 248 illustrated in FIG. 2 includes a frontleft lifter 250 a on the front left damper 202 a and a front rightlifter 250 b on the front right damper 202 b. Although otherconfigurations are possible, in the illustrated example, the front leftdamper 202 a and the front right damper 202 b include a front left coilspring 252 a and a front right coil spring 252 b, respectively, thatextend co-axially and helically about the piston rods of the frontdampers 202 a, 202 b in a coil-over arrangement. The front lifters 250a, 250 b are positioned between the front coils springs 252 a, 252 b andthe first and second rebound chambers 228 a, 228 b of the front dampers202 a, 202 b and extend co-axially and annularly about the piston rods.The manifold assembly 204 further includes a third manifold valve 222 cthat is connected in fluid communication with the pump hydraulic line208. A front axle lift hydraulic line 254 a extends between and isfluidly connected to the third manifold valve 222 c with the front leftlifter 250 a and the front right lifter 250 b. A third pressure sensor224 c is arranged to monitor the fluid pressure in the front axle lifthydraulic line 254 a. Each front lifter 250 a, 250 b is axiallyexpandable such that an increase in fluid pressure inside the frontlifters 250 a, 250 b causes the front lifters 250 a, 250 b to urge thefront coil springs 252 a, 252 b away from the first and second reboundchambers 228 a, 228 b of the front dampers 202 a, 202 b, which operatesto lift (i.e., raise) the front of the vehicle, increasing the rideheight. To activate the front axle lift assembly 248, the suspensioncontrol module 123 opens the third manifold valve 222 c when thebi-directional pump 210 is running in the first direction where thebi-directional pump 210 draws in hydraulic fluid from the reservoirhydraulic line 218 and discharges hydraulic fluid into the pumphydraulic line 208 to produce a positive pressure in the pump hydraulicline 208, which increases fluid pressure in the front axle lifthydraulic line 254 a and thus the front lifters 250 a, 250 b. Once adesired lift position is achieved, the controller closes the thirdmanifold valve 222 c. It should therefore be appreciated that the frontaxle lift assembly 248 can be used to provide improved ground clearanceduring off-road operation or to give low riding vehicles improved groundclearance when traversing speed bumps. To deactivate the front axle liftassembly 248, the suspension control module 123 opens the third manifoldvalve 222 c when the bi-directional pump 210 is running in the seconddirection where the bi-directional pump 210 draws in hydraulic fluidfrom the pump hydraulic line 208 and discharges hydraulic fluid into thereservoir hydraulic line 218 to produce a negative pressure in the pumphydraulic line 208 that reduces fluid pressure in the front axle lifthydraulic line 254 a to lower the front of the vehicle back down to anunlifted position.

FIG. 3 illustrates another suspension system 300 that shares many of thesame components as the suspension systems 100, 200 illustrated in FIGS.1 and 2 , but in FIG. 3 a rear axle lift assembly 356 has been added.Rather than repeat the description set forth above, the followingparagraphs describe the structure and function of the components in FIG.3 that are new and/or different from those shown and described inconnection with FIGS. 1 and 2 . It should be appreciated that thereference numbers in FIG. 1 are “100” series numbers (e.g., 100, 102,104, etc.) and the reference numbers in FIG. 2 are “200” series numbers(e.g., 200, 202, 204, etc.) whereas the components in FIG. 3 that arethe same or similar to the components of the suspension systems 100, 200shown in FIGS. 1 and 2 share the same base reference numbers, but arelisted as “300” series numbers (e.g., 300, 302, 304, etc.). Thus, thesame description for elements 100 and 200 above applies to element 300in FIG. 3 and so on and so forth.

The rear axle lift assembly 356 illustrated in FIG. 3 includes a backleft lifter 350 c on the back left damper 302 c and a back right lifter350 d on the back right damper 302 d. Although other configurations arepossible, in the illustrated example, the back left damper 302 c and theback right damper 302 d include a back left coil spring 352 c and a backright coil spring 352 d, respectively, that extend co-axially andhelically about the piston rods of the back dampers 302 c, 302 d in acoil-over arrangement. The back lifters 350 c, 350 d are positionedbetween the back coils springs 352 c, 352 d and the third and fourthrebound chambers 328 c, 328 d of the back dampers 302 a, 302 b andextend co-axially and annularly about the piston rods. The manifoldassembly 304 further includes a fourth manifold valve 322 d that isconnected in fluid communication with the pump hydraulic line 308. Arear axle lift hydraulic line 354 b extends between and is fluidlyconnected to the fourth manifold valve 322 d with the back left lifter350 c and the back right lifter 350 d. A fourth pressure sensor 324 d isarranged to monitor the fluid pressure in the rear axle lift hydraulicline 354 b. Each back lifter 350 c, 350 d is axially expandable suchthat an increase in fluid pressure inside the back lifters 350 c, 350 dcauses the back lifters 350 c, 350 d to urge the back coil springs 352c, 352 d away from the third and fourth rebound chambers 328 c, 328 d ofthe back dampers 302 c, 302 d, which operates to lift (i.e., raise) theback/rear of the vehicle, increasing the ride height. To activate therear axle lift assembly 356, the suspension control module 123 opens thefourth manifold valve 322 d when the bi-directional pump 310 is runningin the first direction where the bi-directional pump 310 draws inhydraulic fluid from the reservoir hydraulic line 318 and dischargeshydraulic fluid into the pump hydraulic line 308 to produce a positivepressure in the pump hydraulic line 308, which increases fluid pressurein the rear axle lift hydraulic line 354 b and thus the back lifters 350c, 350 d. Once a desired lift position is achieved, the suspensioncontrol module 123 closes the fourth manifold valve 322 d. It shouldtherefore be appreciated that the rear axle lift assembly 356 can beused in combination with the front axle lift assembly 348 (alsodescribed above in connection with FIG. 2 ) to provide improved groundclearance during off-road operation or to give low riding vehiclesimproved ground clearance when traversing speed bumps. To deactivate therear axle lift assembly 356, the suspension control module 123 opens thefourth manifold valve 322 d when the bi-directional pump 310 is runningin the second direction where the bi-directional pump 310 draws inhydraulic fluid from the pump hydraulic line 308 and dischargeshydraulic fluid into the reservoir hydraulic line 318 to produce anegative pressure in the pump hydraulic line 308 that reduces fluidpressure in the rear axle lift hydraulic line 354 b to lower the rear ofthe vehicle back down to an unlifted position.

With reference to FIG. 4 , another suspension system 400 is illustratedthat shares many of the same components as the suspension system 100illustrated in FIG. 1 . Rather than repeat the description set forthabove, the following paragraphs describe the structure and function ofthe components in FIG. 4 that are new and/or different from those shownand described in connection with FIG. 1 . It should be appreciated thatthe reference numbers in FIG. 1 are “100” series numbers (e.g., 100,102, 104, etc.) whereas the components in FIG. 4 that are the same orsimilar to the components of the suspension system 100 shown in FIG. 1share the same base reference numbers, but are listed as “400” seriesnumbers (e.g., 400, 402, 404, etc.). Thus, the same description forelement 100 above applies to element 400 in FIG. 4 and so on and soforth.

The suspension system 400 in FIG. 4 also includes a front left damper402 a, a front right damper 402 b, a back left damper 402 c, and a backright damper 402 d. The suspension system 400 also includes a manifoldassembly 404 that is connected in fluid communication with a pumpassembly 406 by a pump hydraulic line 408. Like in FIG. 1 , the pumpassembly 406 includes a bi-directional pump 410, a hydraulic reservoir412 (e.g., a tank), and a bypass hydraulic line 414 that can be open andclosed by a pressure relief valve 416.

The manifold assembly 404 is connected in fluid communication with thefront and rear dampers 402 a, 402 b, 402 c, 402 d by four hydrauliccircuits 420 a, 420 b, 420 c, 420 d: a first hydraulic circuit 420 a, asecond hydraulic circuit 420 b, a third hydraulic circuit 420 c, and afourth hydraulic circuit 420 d. The manifold assembly 404 includes fourmanifold valves 422 a, 422 b, 422 c, 422 d (a first manifold valve 422a, a second manifold valve 422 b, a third manifold valve 422 c, and afourth manifold valve 422 d) that are connected in parallel with thepump hydraulic line 408. The manifold assembly 404 further includes afirst manifold comfort valve 460 a, a second manifold comfort valve 460b, and six manifold conduits 462 a, 462 b, 462 c, 462 d, 462 e, 462 f: afirst manifold conduit 462 a, a second manifold conduit 462 b, a thirdmanifold conduit 462 c, a fourth manifold conduit 462 d, a fifthmanifold conduit 462 e, and a sixth manifold conduit 462 f. The firstmanifold conduit 462 a is connected in fluid communication with thefirst manifold valve 422 a and the first manifold comfort valve 460 awhile the second manifold conduit 462 b is connected in fluidcommunication with the second manifold valve 422 b and the secondmanifold comfort valve 460 b. The third manifold conduit 462 c isconnected in fluid communication with the third manifold valve 422 c andthe fourth manifold conduit 462 d is connected in fluid communicationwith the fourth manifold valve 422 d. The fifth manifold conduit 462 eis connected in fluid communication with the first manifold comfortvalve 460 a and the sixth manifold conduit 462 f is connected in fluidcommunication with the second manifold comfort valve 460 b. Additionalstructure and operational details of the manifold assembly 404 isdescribed below in connection with FIG. 5 ; however, it should beappreciated from FIG. 4 that fluid pressure in the four hydrauliccircuits 420 a, 420 b, 420 c, 420 d operates to dynamically adjust theroll and pitch stiffness of the vehicle and can be used to eitheraugment or completely replace mechanical stabilizer bars/anti-roll bars.Such mechanical systems require relatively straight, unobstructed runsbetween each of the front dampers 402 a, 402 b and each of the backdampers 402 c, 402 d. Accordingly, the suspension system 400 disclosedherein offers packaging benefits because the dampers 402 a, 402 b, 402c, 402 d only need to be hydraulically connected to the manifoldassembly 404.

The first hydraulic circuit 420 a includes a first cross-over hydraulicline 464 a that extends between and fluidly connects the compressionchamber port 430 b (to the first compression chamber 426 a) of the frontleft damper 402 a and the rebound chamber port 430 a (to the fourthrebound chamber 428 d) of the back right damper 402 d. The firsthydraulic circuit 420 a also includes a first manifold hydraulic line438 a that extends between and fluidly connects the first cross-overhydraulic line 464 a and the first manifold conduit 462 a. The secondhydraulic circuit 420 b includes a second cross-over hydraulic line 464b that extends between and fluidly connects the compression chamber port430 b (to the second compression chamber 426 b) of the front rightdamper 402 b and the rebound chamber port 430 a (to the third reboundchamber 428 c) of the back left damper 402 c. The second hydrauliccircuit 420 b also includes a second manifold hydraulic line 438 b thatextends between and fluidly connects the second cross-over hydraulicline 464 b and the second manifold conduit 462 b. The third hydrauliccircuit 420 c includes a third cross-over hydraulic line 464 c thatextends between and fluidly connects the rebound chamber port 430 a (tothe first rebound chamber 428 a) of the front left damper 402 a and thecompression chamber port 430 b (to the fourth compression chamber 426 d)of the back right damper 402 d. The third hydraulic circuit 420 c alsoincludes a third manifold hydraulic line 438 c that extends between andfluidly connects the third cross-over hydraulic line 464 c and the sixthmanifold conduit 462 f. The fourth hydraulic circuit 420 d includes afourth cross-over hydraulic line 464 d that extends between and fluidlyconnects the rebound chamber port 430 a (to the second rebound chamber428 b) of the front right damper 402 b and the compression chamber port430 b (to the third compression chamber 426 c) of the back left damper402 c. The fourth hydraulic circuit 420 d also includes a fourthmanifold hydraulic line 438 d that extends between and fluidly connectsthe fourth cross-over hydraulic line 464 d and the fifth manifoldconduit 462 e. It should be appreciated that the word “cross-over” asused in the first, second, third, and fourth cross-over hydraulic lines464 a, 464 b, 464 c, 464 d simply means that the first, second, third,and fourth cross-over hydraulic lines 464 a, 464 b, 464 c, 464 d runbetween dampers 402 a, 402 b, 402 c, 402 d at opposite corners of thevehicle (e.g., front left to back right and front right to back left).The first, second, third, and fourth cross-over hydraulic lines 464 a,464 b, 464 c, 464 d need not be linear or arranged in any particulardirection as long as they ultimately connect dampers 402 a, 402 b, 402c, 402 d positioned at opposite corners of the vehicle.

The suspension system 400 also includes four bridge hydraulic lines 440a, 440 b, 440 c, 440 d that fluidly couple the first and third hydrauliccircuits 420 a, 420 c and the second and fourth hydraulic circuits 420b, 420 d to one another. The four bridge hydraulic lines 440 a, 440 b,440 c, 440 d include a front left bridge hydraulic line 440 a thatextends between and fluidly connects the first cross-over hydraulic line464 a and the third cross-over hydraulic line 464 c, a front rightbridge hydraulic line 440 b that extends between and fluidly connectsthe second cross-over hydraulic line 464 b and the fourth cross-overhydraulic line 464 d, a back left bridge hydraulic line 440 c thatextends between and fluidly connects the second cross-over hydraulicline 464 b and the fourth cross-over hydraulic line 464 d, and a backright bridge hydraulic line 440 d that extends between and fluidlyconnects the first cross-over hydraulic line 464 a and the thirdcross-over hydraulic line 464 c.

The front left bridge hydraulic line 440 a is connected to the firstcross-over hydraulic line 464 a between the compression chamber port 430b of the front left damper 402 a and the first manifold hydraulic line438 a and is connected to the third cross-over hydraulic line 464 cbetween the rebound chamber port 430 a of the front left damper 402 aand the third manifold hydraulic line 438 c. The front right bridgehydraulic line 440 b is connected to the second cross-over hydraulicline 464 b between the compression chamber port 430 b of the front rightdamper 402 b and the second manifold hydraulic line 438 b and isconnected to the fourth cross-over hydraulic line 464 d between therebound chamber port 430 a of the front right damper 402 b and thefourth manifold hydraulic line 438 d. The back left bridge hydraulicline 440 c is connected to the second cross-over hydraulic line 464 bbetween the rebound chamber port 430 a of the back left damper 402 c andthe second manifold hydraulic line 438 b and is connected to the fourthcross-over hydraulic line 464 d between the compression chamber port 430b of the back left damper 402 c and the fourth manifold hydraulic line438 d. The back right bridge hydraulic line 440 d is connected to thefirst cross-over hydraulic line 464 a between the rebound chamber port430 a of the back right damper 402 d and the first manifold hydraulicline 438 a and is connected to the third cross-over hydraulic line 464 cbetween the compression chamber port 430 b of the back right damper 402d and the third manifold hydraulic line 438 c. In the illustratedexample, the various hydraulic lines are made of flexible tubing (e.g.,hydraulic hoses), but it should be appreciated that other conduitstructures and/or fluid passageways can be used.

A front left accumulator 442 a is arranged in fluid communication withthe first cross-over hydraulic line 464 a at a location between thecompression chamber port 430 b of the front left damper 402 a and thefront left bridge hydraulic line 440 a. A front right accumulator 442 bis arranged in fluid communication with the second cross-over hydraulicline 464 b at a location between the compression chamber port 430 b ofthe front right damper 402 b and the front right bridge hydraulic line440 b. A back left accumulator 442 c is arranged in fluid communicationwith the fourth cross-over hydraulic line 464 d at a location betweenthe compression chamber port 430 b of the back left damper 402 c and theback left bridge hydraulic circuit 420 c. A back right accumulator 442 dis arranged in fluid communication with the third cross-over hydraulicline 464 c at a location between the compression chamber port 430 b ofthe back right damper 402 d and the back right bridge hydraulic line 440d. Each of the accumulators 442 a, 442 b, 442 c, 442 d have a variablefluid volume that increases and decreases depending on the fluidpressure in the first and second longitudinal hydraulic lines 432 a, 432b. It should be appreciated that the accumulators 442 a, 442 b, 442 c,442 d may be constructed in a number of different ways. For example andwithout limitation, the accumulators 442 a, 442 b, 442 c, 442 d may haveaccumulation chambers and pressurized gas chambers that are separated byfloating pistons or flexible membranes.

The suspension system 400 also includes four electro-mechanical comfortvalves 444 a, 444 b, 444 c, 444 d that are connected in-line (i.e., inseries) with each of the bridge hydraulic lines 440 a, 440 b, 440 c, 440d. A front left comfort valve 444 a is positioned in the front leftbridge hydraulic line 440 a. A front right comfort valve 444 b ispositioned in the front right bridge hydraulic line 440 b. A back leftcomfort valve 444 c is positioned in the back left bridge hydraulic line440 c. A back right comfort valve 444 d is positioned in the back rightbridge hydraulic line 440 d. In the illustrated example, the fourcomfort valves 444 a, 444 b, 444 c, 444 d and the two manifold comfortvalves 460 a, 460 b are semi-active electro-mechanical valves with acombination of passive spring-disk elements and a solenoid. The comfortvalves 444 a, 444 b, 444 c, 444 d and the two manifold comfort valves460 a, 460 b are electronically connected to the suspension controlmodule 123, which is configured to supply electrical current to thesolenoids of the comfort valves 444 a, 444 b, 444 c, 444 d and the twomanifold comfort valves 460 a, 460 b to selectively and individuallyopen and close the comfort valves 444 a, 444 b, 444 c, 444 d and the twomanifold comfort valves 460 a, 460 b.

When the manifold valves 422 a, 422 b, 422 c, 422 d are closed, thehydraulic circuits 420 a, 420 b, 420 c, 420 d operate as a closed loopsystem, either together or separately depending on the open or closedstatus of the comfort valves 444 a, 444 b, 444 c, 444 d and manifoldcomfort valves 460 a, 460 b. When the manifold valves 422 a, 422 b, 422c, 422 d are open, the bi-directional pump 110 either adds or removesfluid from one or more of the hydraulic circuits 420 a, 420 b, 420 c,420 d. There are three primary types of suspension movements that theillustrated suspension system 400 can control either passively (i.e., asa closed loop system) or actively (i.e., as an open loop system) bychanging or adapting the roll and/or pitch stiffness of the vehicle:leaning to one side or the other during cornering (i.e., roll) pitchingforward during braking (i.e., brake dive), and pitching aft duringacceleration (i.e., rear end squat). Descriptions of how the suspensionsystem 400 reacts to each of these conditions are provided below.

When the vehicle is put into a right-hand turn, the momentum of thesprung weight of the vehicle tends to make the vehicle lean left towardsthe outside of the turn, compressing the front left damper 402 a and theback left damper 402 c. When this occurs, fluid flows out from the firstcompression chamber 426 a of the front left damper 402 a and the thirdcompression chamber 426 c of the back left damper 402 c into the firstand fourth cross-over hydraulic lines 464 a, 464 d. As a result of theweight transfer to the left side of the vehicle, the front right damper402 b and back right damper 402 d begin to extend, causing fluid to flowout of the second rebound chamber 428 b of the front right damper 402 band the fourth rebound chamber 428 d of the back right damper 402 d intothe first and fourth cross-over hydraulic lines 464 a, 464 d. When thecomfort valves 444 a, 444 b, 444 c, 444 d are closed, the fluid flow outof the first compression chamber 426 a of the front left damper 402 a,out of the third compression chamber 426 c of the back left damper 402c, out of the second rebound chamber 428 b of the front right damper 402b and out of the fourth rebound chamber 428 d of the back right damper402 d and into the first and fourth cross-over hydraulic lines 464 a,464 d increases the pressure in the front left and back leftaccumulators 442 a, 442 c, thus providing a passive roll resistancewhere it becomes increasingly more difficult to compress the front leftdamper 402 a and the back left damper 402 c since the first compressionchamber 426 a of the front left damper 402 a and the third compressionchamber 426 c of the back left damper 402 c are connected in fluidcommunication with the first and fourth hydraulic circuits 420 a, 420 d.At the same time, fluid flows out of front left and back leftaccumulators 442 b, 442 d and into the first rebound chamber 428 a ofthe front left damper 402 a, into the third rebound chamber 428 c of theback left damper 402 c, into the second compression chamber 426 b of thefront right damper 402 b, and into the fourth compression chamber 426 dof the back right damper 402 d. The resulting pressure differencebetween the dampers 402 a, 402 b, 402 c, 402 d generates damper forcesthat counteract or resist the roll moment of the vehicle. Additionalroll resistance can be added by opening the first manifold valve 422 aand the first manifold comfort valve 460 a as the bi-directional pump410 is running in a first direction where the bi-directional pump 410draws in hydraulic fluid from the reservoir hydraulic line 418 anddischarges hydraulic fluid into the pump hydraulic line 408 to produce apositive pressure in the pump hydraulic line 408, which increases fluidpressure in the first and fourth hydraulic circuits 420 a, 420 d.

The opposite is true when the vehicle is put into a left-hand turn,where the momentum of the sprung weight of the vehicle tends to make thevehicle lean right towards the outside of the turn, compressing thefront right damper 402 b and the back right damper 402 d. When thisoccurs, fluid flows out from the second compression chamber 426 b of thefront right damper 402 b and the fourth compression chamber 426 d of theback right damper 402 d into the second and third cross-over hydrauliclines 464 b, 464 c. As a result of the weight transfer to the right sideof the vehicle, the front left damper 402 a and back left damper 402 cbegin to extend, causing fluid to flow out of the first rebound chamber428 a of the front left damper 402 a and the third rebound chamber 428 cof the back left damper 402 c into the second and third cross-overhydraulic lines 464 b, 464 c. When the comfort valves 444 a, 444 b, 444c, 444 d are closed, the fluid flow out of the second compressionchamber 426 b of the front right damper 402 b, out of the fourthcompression chamber 426 d of the back right damper 402 d, out of thefirst rebound chamber 428 a of the front left damper 402 a, and out ofthe third rebound chamber 428 c of the back left damper 402 c and intothe second and third cross-over hydraulic lines 464 b, 464 c increasesthe pressure in the front right and back right accumulators 142 b, 142d, thus providing a passive roll resistance where it becomesincreasingly more difficult to compress the front right damper 402 b andthe back right damper 402 d since the second compression chamber 426 bof the front right damper 402 b and the fourth compression chamber 426 dof the back right damper 402 d are connected in fluid communication withthe second and third hydraulic circuits 420 b, 420 c. At the same time,fluid flows out of front right and back right accumulators 442 a, 442 cand into the second rebound chamber 428 b of the front right damper 402b, into the fourth rebound chamber 428 d of the back right damper 402 d,into the first compression chamber 426 a of the front left damper 402 a,and into the third compression chamber 426 c of the back left damper 402c. The resulting pressure difference between the dampers 402 a, 402 b,402 c, 402 d generates damper forces that counteract or resist the rollmoment of the vehicle. Additional roll resistance can be added byopening the second manifold valve 422 b and the second manifold comfortvalve 460 b as the bi-directional pump 410 is running in the firstdirection where the bi-directional pump 410 draws in hydraulic fluidfrom the reservoir hydraulic line 418 and discharges hydraulic fluidinto the pump hydraulic line 408 to produce a positive pressure in thepump hydraulic line 408, which increases fluid pressure in the secondand third hydraulic circuits 420 b, 420 c.

During braking, the momentum of the sprung weight of the vehicle tendsto make the vehicle pitch or dive forward, compressing the front leftdamper 402 a and the front right damper 402 b. When this occurs, fluidflows out from the first compression chamber 426 a of the front leftdamper 402 a into the first cross-over hydraulic line 464 a and out fromthe second compression chamber 426 b of the front right damper 402 binto the second cross-over hydraulic line 464 b. As a result of theweight transfer to the front of the vehicle, the back left damper 402 cand back right damper 402 d begin to extend, causing fluid to flow outof the third rebound chamber 428 c of the back left damper 402 c intothe second cross-over hydraulic line 464 b and out of the fourth reboundchamber 428 d of the back right damper 402 d into the first cross-overhydraulic line 464 a. With the front left, front right, back left, andback right comfort valves 444 a, 444 b, 444 c, 444 d and the first andsecond manifold comfort valves 460 a, 460 b all closed, the fluid flowout of the third rebound chamber 428 c of the back left damper 402 c andthe fourth rebound chamber 428 d of the back right damper 402 d into thefirst and second cross-over hydraulic lines 464 a, 464 b increases thepressure in the front left and front right accumulators 442 a, 442 b,thus providing a passive pitch resistance where it becomes increasinglymore difficult to compress the front left damper 402 a and the frontright damper 402 b since the first compression chamber 426 a of thefront left damper 402 a and the second compression chamber 426 b of thefront right damper 402 b are connected in fluid communication with thefirst and second hydraulic circuits 420 a, 420 b.

During acceleration, the momentum of the sprung weight of the vehicletends to make the vehicle pitch or squat rearward (i.e., aft),compressing the back left damper 402 c and the back right damper 402 d.When this occurs, fluid flows out from the third compression chamber 426c of the back left damper 402 c into the fourth cross-over hydraulicline 464 d and out of the fourth compression chamber 426 d of the backright damper 402 d into the third cross-over hydraulic line 464 c. As aresult of the weight transfer to the back/rear of the vehicle, the frontleft damper 402 a and front right damper 402 b begin to extend, causingfluid to flow out of the first rebound chamber 428 a of the front leftdamper 402 a into the third cross-over hydraulic line 464 c and out ofthe second rebound chamber 428 b of the front right damper 402 b intothe fourth cross-over hydraulic line 464 d. With the front left, frontright, back left, and back right comfort valves 444 a, 444 b, 444 c, 444d and the first and second manifold comfort valves 460 a, 460 b allclosed, the fluid flow out of the first rebound chamber 428 a of thefront left damper 402 a and the second rebound chamber 428 b of thefront right damper 402 b into the third and fourth cross-over hydrauliclines 464 c, 464 d increases the pressure in the back left and backright accumulators 442 c, 442 d, thus providing a passive pitchresistance where it becomes increasingly more difficult to compress theback left damper 402 c and the back right damper 402 d since the thirdcompression chamber 426 c of the back left damper 402 c and the fourthcompression chamber 426 d of the back right damper 402 d are connectedin fluid communication with the third and fourth hydraulic circuits 420c, 420 d.

When active or passive roll and/or pitch stiffness is not required, thefour comfort valves 444 a, 444 b, 444 c, 444 d and the two manifoldcomfort valves 460 a, 460 b can be opened to enhance the ride comfort ofthe suspension system 400 and reduce or eliminate unwanted suspensionmovements resulting from the hydraulic coupling of one damper of thesystem to another damper of the system (e.g., where the compression ofone damper causes movement and/or a dampening change in another damper).For example, when the front left comfort valve 444 a is open and thefront left damper 402 a undergoes a compression stroke as the frontwheel hits a bump, fluid may flow from the first compression chamber 426a of the front left damper 402 a, into the first cross-over hydraulicline 464 a, from the first cross-over hydraulic line 464 a to the thirdcross-over hydraulic line 464 c by passing through the front left bridgehydraulic line 440 a and the front left comfort valve 444 a, and intothe first rebound chamber 428 a of the front left damper 402 a. Thus,fluid can travel from the first compression chamber 426 a to the firstrebound chamber 428 a of the front left damper 402 a with the onlyrestriction coming from the dampening valves in the rebound andcompression chamber ports 430 a, 430 b of the front left damper 402 a.As such, when all of the comfort valves 444 a, 444 b, 444 c, 444 d andthe manifold comfort valves 460 a, 460 b are open, the dampers 402 a,402 b, 402 c, 402 d are effectively decoupled from one another forimproved ride comfort. It should also be appreciated that to return thesuspension system 400 to this “comfort mode” of operation, the manifoldvalves 422 a, 422 b, 422 c, 422 d and/or the manifold comfort valves 460a, 460 b may be opened while the bi-directional pump 410 is running in asecond direction where the bi-directional pump 410 draws in hydraulicfluid from the pump hydraulic line 408 and discharges hydraulic fluidinto the reservoir hydraulic line 418 to produce a negative pressure inthe pump hydraulic line 408 that reduces fluid pressure in the hydrauliccircuits 420 a, 420 b, 420 c, 420 d of the suspension system 400.

FIG. 5 illustrates the manifold assembly 404 of the suspension system400 in more detail. The manifold assembly 404 includes first and secondpiston bores 466 a, 466 b that slidingly receive first and secondfloating pistons 468 a, 468 b, respectively. Each floating piston 468 a,468 b includes a piston rod 458 and first and second piston heads 470 a,470 b that are fixably coupled to opposing ends of the piston rod 458. Achamber divider 472 is fixably mounted at a midpoint of each of thefirst and second piston bores 466 a, 466 b. Each chamber divider 472includes a through-bore that slidingly receives the piston rod 458. Assuch, the first piston bore 466 a is divided by the first floatingpiston 468 a into a first piston chamber 474 a that is arranged in fluidcommunication with the first manifold conduit 462 a, a second pistonchamber 474 b disposed between the first piston head 470 a of the firstfloating piston 468 a and the chamber divider 472 in the first pistonbore 466 a, a third piston chamber 474 c disposed between the secondpiston head 470 b of the first floating piston 468 a and the chamberdivider 472 in the first piston bore 466 a, and a fourth piston chamber474 d that is arranged in fluid communication with the fifth manifoldconduit 462 e. Similarly, the second piston bore 466 b is divided by thesecond floating piston 468 b into a fifth piston chamber 474 e that isarranged in fluid communication with the second manifold conduit 462 b,a sixth piston chamber 474 f disposed between the first piston head 470a of the second floating piston 468 b and the chamber divider 472 in thesecond piston bore 466 b, a seventh piston chamber 474 g disposedbetween the second piston head 470 b of the second floating piston 468 band the chamber divider 472 in the second piston bore 466 b, and aneighth piston chamber 474 h that is arranged in fluid communication withthe sixth manifold conduit 462 f. Optionally, biasing members (e.g.,springs) (not shown) may be placed in the second, third, sixth, andseventh piston chambers 474 b, 474 c, 474 f, 474 g to naturally bias thefirst and second floating pistons 468 a, 468 b to a centered positionwhere the second and third piston chambers 474 b, 474 c and the sixthand seventh piston chambers 474 f, 474 g have equal volumes.

The first manifold conduit 462 a is arranged in fluid communication withthe first manifold hydraulic line 438 a, the second manifold conduit 462b is arranged in fluid communication with the second manifold hydraulicline 438 b, the fifth manifold conduit 462 e is arranged in fluidcommunication with the fourth manifold hydraulic line 438 d, and thesixth manifold conduit 462 f is arranged in fluid communication with thethird manifold hydraulic line 438 c. The third manifold conduit 462 c isarranged in fluid communication with the second and sixth pistonchambers 474 b, 474 f while the fourth manifold conduit 462 d isarranged in fluid communication with the third and seventh pistonchambers 474 c, 474 g. As a result, fluid pressure in the fourth pistonchamber 474 d and thus the fifth manifold conduit 462 e can be increasedindependently of the first manifold conduit 462 a by closing the firstmanifold comfort valve 460 a and opening the fourth manifold valve 422 dwhen the bi-directional pump 410 is running in the first direction,which increases pressure in the third piston chamber 474 c and urges thefirst floating piston 468 a to the right in FIG. 5 , decreasing thevolume of the fourth piston chamber 474 d and increasing the pressure inthe fourth piston chamber 474 d. Similarly, fluid pressure in the eighthpiston chamber 474 h and thus the sixth manifold conduit 462 f can beincreased independently of the second manifold conduit 462 b by closingthe second manifold comfort valve 460 b and opening the fourth manifoldvalve 422 d when the bi-directional pump 410 is running in the firstdirection, which increases pressure in the seventh piston chamber 474 gand urges the second floating piston 468 b to the right in FIG. 5 ,decreasing the volume of the eighth piston chamber 474 h and increasingthe pressure in the eighth piston chamber 474 h.

Fluid pressure in the first piston chamber 474 a and thus the firstmanifold conduit 462 a can also be increased without opening the firstmanifold valve 422 a by actuating the first floating piston 468 a, wherethe first manifold comfort valve 460 a is closed and the third manifoldvalve 422 c is open when the bi-directional pump 410 is running in thefirst direction, which increases pressure in the second piston chamber474 b and urges the first floating piston 468 a to the left in FIG. 5 ,decreasing the volume of the first piston chamber 474 a and increasingthe pressure in the first piston chamber 474 a. Similarly, fluidpressure in the fifth piston chamber 474 e and the second manifoldconduit 462 b can also be increased without opening the second manifoldvalve 422 b by actuating the second floating piston 468 b, where thesecond manifold comfort valve 460 b is closed and the third manifoldvalve 422 c is open when the bi-directional pump 410 is running in thefirst direction, which increases pressure in the sixth piston chamber474 f and urges the second floating piston 468 b to the left in FIG. 5 ,decreasing the volume of the fifth piston chamber 474 e and increasingthe pressure in the second piston chamber 474 e.

The manifold assembly 404 may further include a first manifoldaccumulator 476 a that is arranged in fluid communication with the thirdmanifold conduit 462 c between the third manifold valve 422 c and thesecond and sixth piston chambers 474 b, 474 f and a second manifoldaccumulator 476 b that is arranged in fluid communication with thefourth manifold conduit 462 d between the third and seventh pistonchambers 474 c, 474 g. The first and second manifold accumulators 476 a,476 b may be constructed in a number of different ways. For example andwithout limitation, the first and second manifold accumulators 476 a,476 b may have accumulation chambers and pressurized gas chambers thatare separated by floating pistons or flexible membranes. Under braking,fluid flow within the four hydraulic circuits generates a pressuredifference between the first and second manifold accumulators 476 a, 476b, which in turn causes an increase in pressure in the front left andfront right accumulators 442 a, 442 b and provides a pitch stiffnessthat resists the compression of the front dampers 402 a, 402 b andrebound/extension of the back dampers 402 c, 402 d. Under acceleration,fluid flow within the four hydraulic circuits generates an oppositepressure difference between the first and second manifold accumulators476 a, 476 b, which in turn causes an increase in pressure in the backleft and back right accumulators 442 c, 442 d and provides a pitchstiffness that resists the rebound/extension of the front dampers 402 a,402 b and compression of the back dampers 402 c, 402 d. Additional pitchresistance can be added before a braking or acceleration event byopening the third and fourth manifold valves 422 c, 422 d as thebi-directional pump 410 is running in the first direction. Thebi-directional pump 410 draws in hydraulic fluid from the reservoirhydraulic line 418 and discharges hydraulic fluid into the pumphydraulic line 408 to produce a positive pressure in the pump hydraulicline 408, which increases fluid pressure in the first and secondmanifold accumulators 476 a, 476 b. In a similar way, the pitchstiffness of the system can be reduced before a braking or accelerationevent by running the bi-directional pump 410 in the second directionwhile the third and fourth manifold valves 422 c, 422 d.

The manifold assembly 404 may also include six pressure sensors 424 a,424 b, 424 c, 424 d, 424 e, 424 f: a first pressure sensor 424 aarranged to monitor fluid pressure in the first manifold conduit 462 a,a second pressure sensor 424 b arranged to monitor fluid pressure in thesecond manifold conduit 462 b, a third pressure sensor 424 c arranged tomonitor fluid pressure in the third manifold conduit 462 c, a fourthpressure sensor 424 d arranged to monitor fluid pressure in the fourthmanifold conduit 462 d, a fifth pressure sensor 424 e arranged tomonitor fluid pressure in the fifth manifold conduit 462 e, and a sixthpressure sensor 424 f arranged to monitor fluid pressure in the sixthmanifold conduit 462 f. While not shown in FIG. 5 , the pressure sensors424 a, 424 b, 424 c, 424 d, 424 e, 424 f are all electrically connectedto the suspension control module 123.

FIG. 6 illustrates another suspension system 600 that shares many of thesame components as the suspension system 400 illustrated in FIGS. 4 and5 , but in FIG. 6 different pump 610 and manifold assemblies 604 havebeen utilized. Rather than repeat the description set forth above, thefollowing paragraphs describe the structure and function of thecomponents in FIG. 6 that are new and/or different from those shown anddescribed in connection with FIGS. 4 and 5 . It should be appreciatedthat the reference numbers in FIGS. 4 and 5 are “400” series numbers(e.g., 400, 402, 404, etc.) whereas the components in FIG. 6 that arethe same or similar to the components of the suspension system 400 shownin FIGS. 4 and 5 share the same base reference numbers, but are listedas “600” series numbers (e.g., 600, 602, 604, etc.). Thus, the samedescription for element 400 above applies to element 600 in FIG. 6 andso on and so forth.

The pump assembly 606 illustrated in FIG. 6 includes a single directionpump 610 with an inlet port that is connected in fluid communicationwith the hydraulic reservoir 612 by a reservoir hydraulic line 618 andan outlet port that is connected to the pump hydraulic line 608. Inoperation, the single direction pump 610 draws in hydraulic fluid fromthe reservoir hydraulic line 618 via the inlet port and dischargeshydraulic fluid into the pump hydraulic line 608 via the outlet port. Assuch, the single direction pump 610 produces a positive pressure in thepump hydraulic line 608 that can be used by manifold assembly 604 toincrease fluid pressure in the suspension system 600. A check valve 678is positioned in the pump hydraulic line 608 to prevent back feed whenthe single direction pump 610 is turned off. The pump assembly 606 alsoincludes a return hydraulic line 680 that extends from the pumphydraulic line 108 to the hydraulic reservoir 612. A first pump valve682 a is positioned in-line with the return hydraulic line 680. The pumpassembly 606 also includes a pump bridge hydraulic line 683 thatincludes a second pump valve 682 b mounted in-line with the pump bridgehydraulic line 683. The pump bridge hydraulic line 683 connects to thepump hydraulic line 608 at a location between the single direct pump 610and the check valve 678 and connects to the return hydraulic line 680 ata location between the first pump valve 682 a and the hydraulicreservoir 612. In accordance with this arrangement, fluid pressure inthe pump hydraulic line 608 can be increased by turning on the pump 610and closing the second pump valve 682 b and fluid pressure in the pumphydraulic line 608 can be decreased by turning the pump 610 off andopening the first pump valve 682 a.

In the example illustrated in FIG. 6 , only three manifold valves 622 a,622 b, 622 c (i.e., the first manifold valve 622 a, the second manifoldvalve 622 b, and the third manifold valve 622 c) are connected inparallel with the pump hydraulic line 608. The fourth manifold valve 622d is positioned between the first and second piston bores 666 a, 666 band is arranged in fluid communication with the third manifold conduit662 c on one side and the fourth manifold conduit 662 d on the otherside. Thus, to increase fluid pressure in the fifth and/or sixthmanifold conduits 662 e, 662 f independently of the first and secondmanifold conduits 662 a, 662 b, the third and fourth manifold valves 622c, 622 d must be open while the pump 610 is running and the first andsecond manifold comfort valves 660 a, 660 b are closed to increase fluidpressure in the third and seventh piston chambers 674 c, 674 g, whichurges the first and second floating pistons 668 a, 668 b to the right inFIG. 6 decreasing the volume of the fourth and eighth piston chambers674 d, 674 h and increasing the pressure in the fourth and eighth pistonchambers 674 d, 674 h.

FIG. 7 illustrates another suspension system 700 that shares many of thesame components as the suspension system 400 illustrated in FIGS. 4 and5 , but in FIG. 7 a different manifold assembly 704 has been utilized.Rather than repeat the description set forth above, the followingparagraphs describe the structure and function of the components in FIG.7 that are new and/or different from those shown and described inconnection with FIGS. 4 and 5 . It should be appreciated that thereference numbers in FIGS. 4 and 5 are “400” series numbers (e.g., 400,402, 404, etc.) whereas the components in FIG. 7 that are the same orsimilar to the components of the suspension system 400 shown in FIGS. 4and 5 share the same base reference numbers, but are listed as “700”series numbers (e.g., 700, 702, 704, etc.). Thus, the same descriptionfor element 400 above applies to element 700 in FIG. 7 and so on and soforth.

The manifold assembly 704 illustrated in FIG. 7 has the same componentsand hydraulic arrangement as the manifold assembly 404 illustrated inFIGS. 4 and 5 , but in FIG. 7 the placement of the various components ofthe manifold assembly 704 is different to allow the manifold assembly704 to be packaged in the front of the vehicle between the front dampers702 a, 702 b. The manifold assembly 704 illustrated in FIG. 7 includes afront left sub-assembly 784 a and a front right sub-assembly 784 b. Thefront right sub-assembly 784 b includes the first piston bore 766 a, thefirst floating piston 768 a, the first manifold valve 722 a, the thirdmanifold valve 722 c, the first manifold conduit 762 a, and the fifthmanifold conduit 762 e. The front left sub-assembly 784 a includes thesecond piston bore 466 b, the second floating piston 768 b, the secondmanifold valve 722 b, the fourth manifold valve 722 d, the secondmanifold conduit 762 b, and the sixth manifold conduit 762 f. The pumphydraulic line 708 extends between the front left and front rightsub-assemblies 784 a, 784 b and splits to connect to the manifold valves722 a, 722 b, 722 c, 722 d on either side. The third and fourth manifoldconduits 762 c, 762 d extend laterally between the front left and frontright sub-assemblies 784 a, 784 b to connect the second and sixth pistonchambers 774 b, 774 f and the third and seventh piston chambers 774 c,774 g, respectively. It should be appreciated that the order andarrangement of the piston chambers 774 e, 774 f, 774 g, 774 h in thesecond piston bore 766 b shown in FIG. 7 is opposite from that shown inFIGS. 4 and 5 . In other words, in accordance with the arrangement shownin FIG. 7 , the first piston chamber 774 a (which is connected in fluidcommunication with the first manifold conduit 762 a) faces the fifthpiston chamber 774 e (which is connection in fluid communication withthe second manifold conduit 762 b). In other words, in FIG. 7 the fifthpiston chamber 774 e (which is connection in fluid communication withthe second manifold conduit 762 b) is to the right of the eighth pistonchamber 774 h (which is connected in fluid communication with the sixthmanifold conduit 762 f), whereas in FIGS. 4 and 5 the fifth pistonchamber 474 e (which is connected in fluid communication with the secondmanifold conduit 462 b) is to the left of the eighth piston chamber 474h (which is connected in fluid communication with the sixth manifoldconduit 462 f). This reversal of the arrangement of the piston chambers774 e, 774 f, 774 g, 774 h in the second piston bore 766 b simplifiesand shortens the runs required for the manifold hydraulic lines 738 a,738 b, 738 c, 738 d and is therefore advantageous.

FIG. 8 includes a functional block diagram of an example implementationof the suspension control module 123. A pump control module 804 receivespower from a battery 808 of the vehicle. The pump control module 804controls operation, speed, and direction of operation of a pump 812 ofthe suspension system. More specifically, the pump control module 804controls application of power to the pump 812 of the suspension system.Examples of the pump 812 are discussed above. For example, in theexamples of FIGS. 1-4 , the pump control module 804 controls applicationof power to the pump 110, 210, 310, or 410. In the examples of FIGS. 6and 7 , the pump control module 804 controls application of power to thepump 610 or 710. The pump control module 804 may control, for example, apolarity of power applied to the pump 812, a frequency of power appliedto the pump 812, a magnitude of voltage applied to the pump 812, and/ora current through the pump 812.

A valve control module 816 controls actuation (e.g., opening andclosing) of valves 820 of the suspension system. Examples of the valves820 are discussed above with respect to examples of FIGS. 1-7 . Forexample, the valve control module 816 controls actuation of the valves122 a, 122 b, 144 a-c, and 146 a-b in the example of FIG. 1 .

Referring back to FIG. 1 , the tank 112 may be not accessible to addhydraulic fluid into the suspension system or to remove hydraulic fluidfrom the system. The tank 112 may not include a port, opening, inlet,nozzle, etc. through which hydraulic fluid can be externally input tothe tank 112 or externally removed from the tank 112.

As such, the suspension system may include a quick connect valve 160.The quick connect valve 160 may be fluidly connected, for example, tothe line 132 a or in another suitable location. While the quick connectvalve 160 is shown in the example of FIG. 1 , the quick connect valve160 can be included in all of the suspension systems above and thefollowing is also applicable to all of the example embodiments shown anddescribed. In various implementations, two or more quick connect valvesmay be included.

An external pump can be connected to the quick connect valve 160 via ahydraulic line, such as to fill the suspension system with hydraulicfluid and/or to pump hydraulic fluid out of the suspension system. Invarious implementations, the pump 812 may be used to pump hydraulicfluid out of the suspension system.

A service module 176 may control operation of the external pump andperformance of one or more operations. The service module 176 may, forexample, connect to an on board diagnostic (OBD) port of the vehicle.Via the OBD port, the service module 176 may coordinate control ofvarious components with the suspension control module 123, receive oneor more operating parameters (e.g., pressures measured by the pressuresensors discussed above), and perform one or more other functions.

Referring back to FIG. 8 , a communication module 824 may communicatewith the service module 176 using a communication protocol, such as acar area network (CAN) bus communication protocol or another suitablecommunication protocol.

A grading module 828 may control operation of the pump 812 and actuationof the valves 820 to determine a grade indicative of how well thesuspension system is filled with hydraulic fluid. The grade may be, forexample, a value between 0 and 100. The grade may increase (improve) asthe amount of hydraulic fluid in the suspension system increases and theamount of air in the suspension system decreases, and vice versa.

Determination of the grade is performed using pressures measured bypressure sensors 840, such as the pressure sensors 124 a-b in theexample of FIG. 1 , the pressure sensors 224 a-c in the example of FIG.2 , the pressure sensors 324 a-d in the example of FIG. 3 , or thepressure sensors of the examples of FIGS. 4, 5, 6, or 7 . The gradingmodule 828 operates the pump 812 in the second direction to decreasepressure within the suspension system and records the measured pressuresonce all of the pressures are less than or equal to a firstpredetermined pressure (a predetermined low pressure). The gradingmodule 828 also operates the pump 812 in the first direction to increasepressure within the suspension system and records the measured pressuresonce all of the pressures are greater than or equal to a secondpredetermined pressure (a predetermined high pressure). The secondpredetermined pressure is greater than the first predetermined pressure.The grading module 828 determines a volume of air within the suspensionsystem based on the recorded pressures, and determines the grade basedon the volume of air.

FIG. 9 is a functional block diagram of an example implementation of thegrading module 828. A command module 904 generates commands foroperation of the pump 812 and actuation of the valves 820 for the gradedetermination. The pump control module 804 controls the pump 812according to the pump command, and the valve control module 816 actuatesthe valves 820 according to the valve command. In this manner, thegrading module 828 controls the pump 812 and the valves 820 for thegrade determination.

The command module 904 may start the grade determination in response toreceipt of a start signal, such as from the service module 176. Theservice module 176 may generate the start signal, for example, inresponse to receipt of user input indicative of a request to determine agrade for the filling of the suspension system or in response to anotherevent, such as the suspension system being filled.

When the start signal is received, the command module 904 may open allof the valves 820 and operate the pump 812 in the second direction. Thisdecreases the pressures measured by the pressure sensors 840 within thesuspension system.

A monitoring module 908 monitors the pressures while the pump 812 isoperating in the second direction and records (stores) the pressures(low pressures) in memory 912 when all of the pressures are less than orequal to the first predetermined pressure. For example only, the firstpredetermined pressure may be approximately 5-10 bar or another suitablepressure.

When the pressures have been recorded, the command module 904 operatesthe pump 812 in the first direction. This increases the pressuresmeasured by the pressure sensors 840. The monitoring module 908 monitorsthe pressures while the pump 812 is operating in the first direction andrecords (stores) the pressures (high pressures) in memory 912 when allof the pressures are greater than or equal to the second predeterminedpressure. For example only, second predetermined pressure may be, forexample, approximately 25-60 bar or another suitable pressure.

The monitoring module 908 also determines a volumetric flowrate of thepump 812 while the pump 812 is operating in the first direction. Themonitoring module 908 may determine the volumetric flow rate, forexample, based on a pressure within the suspension system (e.g., 124 aor 124 b in the example of FIG. 1 ), a voltage applied to an electricmotor of the pump 812, a current of the motor of the pump 812, and atemperature of the motor of the pump 812. A temperature sensor 916 maymeasure the temperature of the motor. A current sensor 920 may measurethe current of the motor. A voltage sensor 924 may measure the voltageof the motor. The monitoring module 908 may determine the volumetricflow rate using one of an equation and a lookup table that relatespressures, currents, temperatures, and voltages to volumetric flowrates.

The monitoring module 908 also determines a volume of hydraulic fluidinput to the suspension system based on the volumetric flow rate. Themonitoring module 908 may, for example, determine the volume bydetermining a mathematical integral of the volumetric flowrate. Themonitoring module 908 also updates a total volume (of hydraulic fluid)input to the suspension system since operation of the pump 812 in thefirst direction began. The monitoring module 908 may, for example, addthe volume (determined by integrating the volumetric flow rate) to aprevious value of the total volume input to update the total volumeinput. The total volume input therefore increases over time as hydraulicfluid is pumped into the suspension system.

An air module 928 determines a volume of air within the suspensionsystem based on the low pressures, the high pressures, and the totalvolume input to the suspension system to increase the pressures to thesecond predetermined pressure. The air module 928 determines the volumeof air using one of an equation and a lookup table that relates lowpressures, high pressures, and total volumes to volumes of air given thepredetermined (known) total volume of the suspension system. In variousimplementations, the air module 928 may average the low pressures,average the high pressures, and determine the volume of air based on theaverage of the low pressures, the average of the high pressures, and thetotal volume input.

A grade module 932 determines the grade based on the predetermined totalvolume of the suspension system and the volume of air in the suspensionsystem. The grade module 932 may determine the grade using one of alookup table and an equation that relates volumes of air and totalvolumes to grades. For example, the grade module 932 may set the gradeusing the equation:

$Grade = \frac{VT - VA}{VT} \ast 100,$

where VT is the predetermined total volume of the suspension system, VAis the volume of air in the suspension system, and 100 is a scalar thatadjusts the grade to a value between 0 and 100, inclusive. The gradeincreases as the volume of air decreases and vice versa.

In various implementations, the grade module 932 may determine a volumeof the hydraulic fluid within the suspension system based on thepredetermined total volume and the volume of air in the suspensionsystem. For example, the grade module 932 may determine the volume ofhydraulic fluid using an equation or a lookup table that relates volumesof air to volumes of hydraulic fluid given the predetermined totalvolume of the suspension system. For example only, the grade module 932may set the volume of hydraulic fluid using the equation:

VT − VA = VH,

where VH is the volume of hydraulic fluid, VT is the predetermined totalvolume, and VA is the volume of air in the suspension system.

The grade module 932 may determine the grade based on the predeterminedtotal volume of the suspension system and the volume of hydraulic fluidin the suspension system. The grade module 932 may determine the gradeusing one of a lookup table and an equation that relates volumes ofhydraulic and total volumes to grades. For example, the grade module 932may set the grade using the equation:

$Grade = \frac{VH}{VT} \ast 100,$

where VT is the predetermined total volume of the suspension system, VHis the volume of hydraulic fluid in the suspension system, and 100 is ascalar that adjusts the grade to a value between 0 and 100, inclusive.The grade increases as the volume of hydraulic fluid increases and viceversa.

An indicator module 936 indicates whether the filling of the suspensionsystem is adequate or not based on the grade. For example, the indicatormodule 936 may indicate a fault in the filling when the grade is lessthan a predetermined value. The indicator module 936 may indicate thatthe filling is acceptable when the grade is greater than or equal to thepredetermined value.

The indicator module 936 may take one or more actions. For example, theindicator module 936 may transmit the indicator to the service module176 for display on a display of the service module 176. Additionally oralternatively, the indicator module 936 may store the indicator in thememory 912. One or more other actions may additionally or alternativelybe taken based on the indicator.

FIG. 10 is a flowchart depicting an example method of determining thegrade for filling of the suspension system with hydraulic fluid. Controlbegins with 1004 where the command module 904 determines whether tostart the determination of the grade. The command module 904 maydetermine to start, for example, in response to receipt of the startsignal, in response to a signal indicative of completion of a filling ofthe suspension system, or in response to another suitable event. If 1004is true, control continues with 1008. If 1004 is false, control mayremain at 1004.

At 1008, the command module 904 opens the valves 820 and operates thepump 812 in the second direction to decrease pressure within thesuspension system. At 1012, the monitoring module 908 determines whetherthe pressures measured by the pressure sensors 840 are less than orequal to the first predetermined pressure (low pressure). If 1012 istrue, control continues with 1020. If 1012 is false, control transfersto 1016. At 1016, the command module 904 may determine whether a periodsince a first instance of 1008 is greater than a first predeterminedperiod. The first predetermined period may be, for example, 1-5 minutesor another suitable period. If 1016 is true, the command module 904 maydisable the pump 812 and close the valves 820 and end the grading. Theindicator module 936 may also indicate that the grading failed, such asby storing an indicator that the grading failed in memory and/ortransmitting the indicator that the grading failed to the service module176. If 1016 is false, control returns to 1008 to continue decreasingpressure within the suspension system.

At 1020, the monitoring module 908 may wait a predetermined period(e.g., 15-30 seconds), and the monitoring module 908 stores the presentpressure measurements of the pressure sensors 840 in the memory 912 aslow pressures if all of the pressures are within a predetermined amount(e.g., +/- 0/5 bar). If all of the pressures are not within thepredetermined amount, control may return to 1004. Waiting thepredetermined period allows the pressures to settle.

At 1024, the command module 904 operates the pump in the first directionand maintains the valves 820 open. This should increase the pressuresmeasured by the pressure sensors 840. Also at 1024, the monitoringmodule 908 also determines the volumetric flowrate of the pump 812,determines a volume pumped by the pump 812 by integrating the volumetricflowrate, and updates a total volume input (pumped by the pump 812 inthe first direction since operation in the first direction began) byadding the volume pumped to the previous value of the total volumeinput.

At 1028, the monitoring module 908 determines whether the pressuresmeasured by the pressure sensors 840 are greater than the firstpredetermined pressure (low pressure). If 1028 is true, controlcontinues with 1036. If 1028 is false, control transfers to 1032. At1032, the command module 904 may determine whether a period since afirst instance of 1024 is greater than a second predetermined period.The second predetermined period may be, for example, 1-5 minutes oranother suitable period. The second predetermined period may be the sameas or different than the first predetermined period. If 1032 is true,the command module 904 may disable the pump 812 and close the valves 820and end the grading. The indicator module 936 may also indicate that thegrading failed, such as by storing an indicator that the grading failedin memory and/or transmitting the indicator that the grading failed tothe service module 176. If 1032 is false, control returns to 1024 tocontinue increasing pressure within the suspension system.

At 1036, the monitoring module 908 may wait a predetermined period(e.g., 15-30 seconds), and the monitoring module 908 stores the presentpressure measurements of the pressure sensors 840 in the memory 912 ashigh pressures if all of the pressures are within a predetermined amount(e.g., +/- 0/5 bar). If all of the pressures are not within thepredetermined amount, control may return to 1004. Waiting thepredetermined period allows the pressures to settle. The monitoringmodule 908 also stores the total volume input in the memory 912.

At 1040, the command module 904 disables the pump 812 (e.g., disconnectsthe pump 812 from power) and closes the valves 820. At 1044, the airmodule 928 determines the volume of air in the suspension system. Forexample, the air module 928 may determine the volume of air in thesuspension system using the equation:

$VA = \frac{Plow \ast Phigh}{Patm( {Phigh - Plow} )} \ast Vpump - Vcorr$

where VA is the volume of air, Plow is the average of the low pressures,Phigh is the average of the high pressures, Patm is the atmospheric airpressure, Vpump is the total volume input, and Vcorr is a volumecorrection. The atmospheric air pressure (Patm) may be a fixedpredetermined value or may be measured using a sensor. The volumecorrection (Vcorr) may be a fixed predetermined value. As an alternativeto using the averages, a highest or lowest one of the high pressures,and/or a highest or lowest one of the low pressures may be used.

At 1048, the grade module 932 determines the grade, as described above.At 1052, the indicator module 936 determines whether the grade isgreater than the predetermined value. With the example grades discussedabove as being values between 0 and 100, the predetermined value may be,for example approximately 92 (corresponding to 92 percent of thesuspension being filled with hydraulic fluid) or another suitable value.Approximately may mean +/- 10 percent. If 1052 is true, the indicatormodule 936 indicates that the filling is satisfactory (e.g., sets anindicator to a first state) at 1060, and control may end. If 1052 isfalse, the indicator module 936 indicates that the filling failed (e.g.,sets an indicator to a second state) at 1056, and control may end. Invarious implementations, one or more actions may be taken when thefilling failed, such as described above.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In the figures, the direction of an arrow, as indicated by thearrowhead, generally demonstrates the flow of information (such as dataor instructions) that is of interest to the illustration. For example,when element A and element B exchange a variety of information butinformation transmitted from element A to element B is relevant to theillustration, the arrow may point from element A to element B. Thisunidirectional arrow does not imply that no other information istransmitted from element B to element A. Further, for information sentfrom element A to element B, element B may send requests for, or receiptacknowledgements of, the information to element A.

In this application, including the definitions below, the term “module”or the term “controller” may be replaced with the term “circuit.” Theterm “module” may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks,flowchart components, and other elements described above serve assoftware specifications, which can be translated into the computerprograms by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language), XML (extensible markuplanguage), or JSON (JavaScript Object Notation) (ii) assembly code,(iii) object code generated from source code by a compiler, (iv) sourcecode for execution by an interpreter, (v) source code for compilationand execution by a just-in-time compiler, etc. As examples only, sourcecode may be written using syntax from languages including C, C++, C#,Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl,Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5threvision), Ada, ASP (Active Server Pages), PHP (PHP: HypertextPreprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, VisualBasic®, Lua, MATLAB, SIMULINK, and Python®.

What is claimed is:
 1. A system for grading filling of a suspensionsystem with hydraulic fluid, the system comprising: a pump controlmodule configured to: during a first period, operate an electric pump ofthe suspension system in a first direction and decrease hydraulic fluidpressure within the suspension system; and during a second period,operate the electric pump of the suspension system in a second directionand increase hydraulic fluid pressure within the suspension system; amonitoring module configured to: store a first pressure of hydraulicfluid within the suspension system measured using a pressure sensor whenthe first pressure is less than or equal a first predetermined pressurewhile the pump is operated in the first direction; and store a secondpressure of hydraulic fluid within the suspension system measured usingthe pressure sensor when the second pressure is greater than or equal asecond predetermined pressure while the pump is operated in the seconddirection; and a grade module configured to determine a grade value forfilling of the suspension system with hydraulic fluid based on the firstpressure and the second pressure.
 2. The system of claim 1 wherein thesecond predetermined pressure is greater than the first predeterminedpressure.
 3. The system of claim 1 wherein the first period is beforethe second period.
 4. The system of claim 1 further comprising anindicator module configured to: set an indicator to a first state whenthe grade value is greater than a predetermined value; and set theindicator to a second state when the grade value is less than thepredetermined value.
 5. The system of claim 1 further comprising an airmodule configured to determine a volume of air in the suspension systembased on the first pressure and the second pressure, wherein the grademodule is configured to determine the grade value for filling of thesuspension system with hydraulic fluid based on the volume of air in thesuspension system.
 6. The system of claim 5 wherein the grade module isconfigured to: decrease the grade value as the volume of air increases;and increase the grade value as the volume of air decreases.
 7. Thesystem of claim 5 wherein the grade module is configured to determinethe grade value for filling of the suspension system with hydraulicfluid based on the volume of air in the suspension system and apredetermined total volume of the suspension system.
 8. The system ofclaim 7 wherein the grade module is configured to set the grade valuebased on the equation: $\frac{Vt - Va}{Vt},$ where Vt is thepredetermined total volume of the suspension system and Va is the volumeof air in the suspension system.
 9. The system of claim 1 wherein thegrade module is configured to: determine a volume of hydraulic fluid inthe suspension system based on the first pressure and the secondpressure; and determine the grade value for filling of the suspensionsystem with hydraulic fluid based on the volume of hydraulic fluid inthe suspension system.
 10. The system of claim 9 wherein the grademodule is configured to: decrease the grade value as the volume of airincreases; and increase the grade value as the volume of air decreases.11. The system of claim 9 wherein the grade module is configured todetermine the grade value for filling of the suspension system withhydraulic fluid based on the volume of oil in the suspension system anda predetermined total volume of the suspension system.
 12. The system ofclaim 11 wherein the grade module is configured to set the grade valuebased on the equation: $\frac{Vh}{Vt},$ where Vt is the predeterminedtotal volume of the suspension system and Vh is the volume of hydraulicfluid in the suspension system.
 13. A method of grading filling of asuspension system with hydraulic fluid, the method comprising: during afirst period, operating an electric pump of the suspension system in afirst direction and decrease hydraulic fluid pressure within thesuspension system; during a second period, operating the electric pumpof the suspension system in a second direction and increase hydraulicfluid pressure within the suspension system; storing a first pressure ofhydraulic fluid within the suspension system measured using a pressuresensor when the first pressure is less than or equal a firstpredetermined pressure while the pump is operated in the firstdirection; storing a second pressure of hydraulic fluid within thesuspension system measured using the pressure sensor when the secondpressure is greater than or equal a second predetermined pressure whilethe pump is operated in the second direction; and determining a gradevalue for filling of the suspension system with hydraulic fluid based onthe first pressure and the second pressure.
 14. The method of claim 13wherein the second predetermined pressure is greater than the firstpredetermined pressure.
 15. The method of claim 13 wherein the firstperiod is before the second period.
 16. The method of claim 13 furthercomprising: setting an indicator to a first state when the grade valueis greater than a predetermined value; and setting the indicator to asecond state when the grade value is less than the predetermined value.17. The method of claim 13 further comprising determining a volume ofair in the suspension system based on the first pressure and the secondpressure, wherein determining the grade value includes determining thegrade value for filling of the suspension system with hydraulic fluidbased on the volume of air in the suspension system.
 18. The method ofclaim 17 wherein determining the grave value includes: decreasing thegrade value as the volume of air increases; and increasing the gradevalue as the volume of air decreases.
 19. The method of claim 5 whereindetermining the grade value includes determining the grade value forfilling of the suspension system with hydraulic fluid based on thevolume of air in the suspension system and a predetermined total volumeof the suspension system.
 20. The method of claim 19 wherein determiningthe grade value includes setting the grade value based on the equation:$\frac{Vt - Va}{Vt},$ where Vt is the predetermined total volume of thesuspension system and Va is the volume of air in the suspension system.